This invention relates to the enhancement of the humectancy of skin conditioning compositions with certain organosilicon compounds. More particularly, certain glyceroxyfunctional organosilicon compounds are included as an ingredient in a skin conditioner.
Mineral oil is a highly refined, colorless, tasteless, and odorless, liquid mixture of hydrocarbons obtained from petroleum, that has been used medicinally as an internal lubricant and in the manufacture of various salves and ointments. It is also known as medicinal oil, white mineral oil, heavy mineral oil, light mineral oil, liquid paraffin, and paraffin oil. Mineral oil has long been the emollient of choice in creams and lotions. It is second only to water as a moisturizer ingredient. Mineral oil acts as a moisturizer primarily through the functioning of the ingredient as an occlusive barrier. The water content of the outer layers of the stratum corneum of the human skin is a controlling factor in the appearance of dry skin symptoms. When the stratum corneum contains an adequate amount of water within the range of ten to twenty percent, the skin remains flexible. However, when the water content falls below ten percent, the stratum corneum often becomes brittle and rough, and can exhibit scaling and cracking.
The stratum corneum receives its water from the deep layers of the epidermis by diffusion or when it is brought into direct contact with water. The diffusion process is controlled by the water content of the skin, as well as the concentration gradient. In a very dry environment, the water loss from the external skin layers can be significant and often exceeds the rate of replacement by diffusion. An occlusive barrier of mineral oil, for example, placed onto the surface of the skin acts to retard the water loss to the environment and allows the skin surface to rehydrate by the diffusion process. Due to the effectiveness, low cost, and safety, of petroleum derivatives such as mineral oil, it serves as a useful occlusive moisturizer and contributes to dry skin prevention by protection and moisture retention, as well as dry skin repair by emolliency, lubricity, and moisture restoration.
While mineral oil has been found to be an effective and economical emollient for skin care applications, and provides softening, smoothing, and a protective action on skin, it nevertheless suffers from the disadvantage that it is easily removed from the skin by washing the skin with soap. Thus, the effectiveness and long term benefits of mineral oil enumerated above are of a limited duration.
Accordingly, it is not uncommon to include in skin conditioning compositions a humectant which is capable of introducing moisture to the skin from the atmosphere in conditions of moderate or high humidity. In conditions of low humidity, humectants attract moisture from the lower layers of the skin. Humectants are materials which are hygroscopic therefore and capable of retaining moisture. Among the most well known water retentive humectant capable of preventing drying out is glycerol. Glycerol is known to be an effective humectant and is generally considered harmless in cosmetic applications. It is a clear, water-white viscous liquid having the chemical formula HOCH.sub.2 CHOHCH.sub.2 OH. Glycerol exhibits no bonding to the skin and hence is not substantive and can be washed from the skin surface. It is used in many creams and lotions for the purpose of keeping the skin soft and replacing skin moisture. Technically, the term glycerol connotes the pure compound 1,2,3-propanetriol whereas the term glycerin implies a product containing in excess of about ninety-five percent glycerol.
In accordance with the present invention, a novel delivery mechanism for glycerol has been discovered in which a reaction product is formed resulting in a glyceroxyfunctional organosilicon compound. Upon application to the skin, the reaction product hydrolyzes to release free glycerol. Organosilicon compounds which include the glyceroxy radical are not new. For example, in U.S. Pat. No. 3,741,917, issued Jun. 26, 1973; U.S. Pat. No. 3,933,407, issued Jan. 20, 1976; and U.S. Pat. No. 4,122,029, issued Oct. 24, 1978; there are described certain dimethylsiloxane copolymers which contain an intervening oxyalkylene group between the silicon atom on the main siloxane chain and the glyceroxy radical. In contrast, the compositions of the present invention include a glyceroxy radical directly bonded to the silicon atom on the main chain to form either silanes substituted with glyceroxy groups or dimethylsiloxane polymers substituted with glyceroxy groups.